Bill, thanks for your writeup on the Marantz units -- they're close to my heart . . . both my posted systems feature Model 2s, and I've owned 1s, 8s, and 9s in the past; truly inspirational stuff.
A quick response to your comment on the internal wiring . . . sometimes what may look haphazard at first can actually reveal some beautiful subleties upon further examination -- an example is the power-supply and ground wiring inside the Model 2.
The Model 2 (and 5 also) use an arrangement that I view as being in between a choke-input and a cap-input topology; it's cap-input, but the first capacitor is a low-value (8uF) oil-filled industrial type, with aluminum electrolytics used only after the choke. In practice this gives much of the superior load regulation of the choke-input type, but closer to the voltage-efficiency of the cap-input approach. Rectifier tube life and inrush damping are much better with this design, as the rectifier tube(s) only directly see a small amount of capacitance.
But my favorite subtlety of this design is the fast that the vast majority of the ripple current, especially the higher-frequency harmonics, are bypassed with a capacitor that is well suited to the application - the industrial oil type. The ripple current across the aluminum electrolytic is then far lower, dramatically increasing their life. And if you take a look at how the ground wiring is laid out through this section, it's immediately obvious that they understood this - because it's laid out in such a manner so that the ripple current (even on the ground side) is kept out of the plate supply.
I think this is one of the many reasons why my Model 2s are absolutely dead quiet, with no hum, even with my ear within a couple of inches of a reasonably sensitive loudspeaker.
A quick response to your comment on the internal wiring . . . sometimes what may look haphazard at first can actually reveal some beautiful subleties upon further examination -- an example is the power-supply and ground wiring inside the Model 2.
The Model 2 (and 5 also) use an arrangement that I view as being in between a choke-input and a cap-input topology; it's cap-input, but the first capacitor is a low-value (8uF) oil-filled industrial type, with aluminum electrolytics used only after the choke. In practice this gives much of the superior load regulation of the choke-input type, but closer to the voltage-efficiency of the cap-input approach. Rectifier tube life and inrush damping are much better with this design, as the rectifier tube(s) only directly see a small amount of capacitance.
But my favorite subtlety of this design is the fast that the vast majority of the ripple current, especially the higher-frequency harmonics, are bypassed with a capacitor that is well suited to the application - the industrial oil type. The ripple current across the aluminum electrolytic is then far lower, dramatically increasing their life. And if you take a look at how the ground wiring is laid out through this section, it's immediately obvious that they understood this - because it's laid out in such a manner so that the ripple current (even on the ground side) is kept out of the plate supply.
I think this is one of the many reasons why my Model 2s are absolutely dead quiet, with no hum, even with my ear within a couple of inches of a reasonably sensitive loudspeaker.